1. Field of the Invention
The present invention relates to a handling apparatus for lifting, moving, mounting, etc., an object in a two-dimensional region, and, in particular, to a safety mechanism for such an apparatus.
2. Description of the Related Art
In a handling apparatus having two degrees of freedom, there is a case wherein the movement of a holding member for holding an object need be controlled so that the holding member can move along a predetermined locus. For example, there is a handling apparatus wherein a hand arm is attached, via rotational moving means, to an elevation mechanism movable along vertical moving means, and a carrier holding member for holding a wafer carrier containing a plurality of semiconductor wafers is attached to an end portion of this hand arm. In the case where the wafer is moved between a loading/unloading table and a stock section within a clean stocker by using this handling apparatus, it is necessary, in order to reduce to a minimum the space where the wafer carrier is moved, to synchronize the movement of the vertical moving means and that of the rotational moving means and vertically move and rotate the carrier holding member, thereby to move the wafer carrier in the horizontal direction.
In general, as means for satisfying this demand, a control system is employed wherein an increment from the initial positions of vertical moving means and rotational moving means is detected by encoders provided on both moving means and the synchronous movement of the vertical moving means and rotational moving means is controlled based on the detected increment.
However, in this type of conventional handling apparatus, since the synchronous movement of the vertical moving means and rotational moving means is controlled by the encoders, it is highly possible that, when the movement of the carrier holding member deviates from a predetermined locus owing to an abnormality of the hardware or software, the handling apparatus may contact or collide other peripheral devices.
In addition, in this conventional apparatus, the moving means are controlled based on the increment from the initial positions thereof. Thus, when it becomes impossible to identify the current positions of the moving means, for example, because the apparatus is stopped in the course of operation, the operation of the apparatus becomes impossible thereafter.